One of the biggest questions surrounding XMRV is transmission. Viruses don’t just jump up and attack people – they need to be transmitted. Because it’s clear that this virus is not spread through the air which means it needs to be transmitted from human to human either via the saliva, blood, semen or mother’s milk or some other way.
The presence of XMRV in the blood potentially puts the blood supply at risk and is no doubt driving a lot of research at the NIH. (Will ME/CFS patients be advised not to give blood? Will they at some point not be allowed to give blood?)
The presence of the virus in saliva, semen and other bodily fluids provides several potential avenues of transmission. Simply the presence of a virus in say, the saliva, does not mean it can be transmitted in the saliva. HIV, for instance, is found in the saliva but is not transmitted in the saliva.
Dr. Cheney flatly asserted, however, that the virus is transmissible by all bodily fluids and believes this is why it has a higher infectivity rates than the other known human retroviruses (which tend to have low infectious rates).
Dr. Klimas, a noted chronic fatigue syndrome and AIDS researcher and physician, has given probably the most complete answer we have at this point. In a blog in the New York Times she stated that retroviruses are generally spread sexually, by blood transfusions or from the mother to the fetus.
She pointed out that we already know quite a bit about the ‘infectious rate’ of chronic fatigue syndrome. It’s rare for partners or close family members of chronic fatigue syndrome patients to have this disease or for it to be passed from mother to child.
This suggests that infectivity rates in general are quite low by whatever means. Dr. Coffin, a molecular biologist from Tufts University notes that the evidence for sexual transmission is indirect and that conclusions about sexual transmission are ‘premature’.
Even if a virus is theoretically transmissible via a certain pathway it’s infectious potential can drop markedly if a person’s viral loads are low. We don’t as yet know anything about how much virus (ie viral load) was found in the WPI study. Patients could have high viral loads (i.e. be great infectious) or low viral loads (not be very infectious).